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b=bqs1FXjS13wNgcrsExd9ewUN58pNMxoAP7eGdSlYnjyF9xKfP2iBHfxOe2KfZVREM 9gxfVARpua7JlcnWeFDB36Ex/f7obduxKx7a0GCETaRR9lUsUihaUKvaK18xEp9oXQ EY0CpVjwQJzDNGZVmxxjeVnj4xgCbadZtPEi+x6O7czh1R5FJzdEmTz2myEDvJV5r5 qBXv/Sp+zgF4dzaeaYRg1oDi+w5cSztHW6FsrRzRsCQnX51ZZY4sObGOlPDyPUTaaJ ileYHXScFqnzAik6050zNfYLeWzMHmZI+BsS7c9EbmjnQ3tlKrKYq/ykTeRAnIJPO3 cL2zQ6WDr2C6g== Message-ID: Date: Fri, 8 May 2026 13:46:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] dma-contiguous: setup default numa cma area if not configured explicitly To: Feng Tang Cc: Marek Szyprowski , Robin Murphy , Ying Huang , Andrew Morton , Lorenzo Stoakes , Liam.Howlett@oracle.com, Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , linux-mm@kvack.org, Christoph Hellwig , Catalin Marinas , Will Deacon , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, Changrong Chen References: <20260428060550.7167-1-feng.tang@linux.alibaba.com> <6dd52f8b-7092-4d02-ba24-f8b55409b7b6@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: AC8871C000B X-Rspamd-Server: rspam04 X-Stat-Signature: m7rjgzzyot1i5iw9pcgofryjmkzmm74o X-HE-Tag: 1778240771-159922 X-HE-Meta: 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 dJmRlRPp F0gTRBtHBNhy7CF/Q2MI/qVYJcfH6gHrOVAvG4V5UoZ5029Mvx9SjHTjfgAUUjZOD4tXKc71UtvS57d0nVfIUI9gSQC80s9qhgrYRlpfco8S4T03lO6oM6KvzqAXoEpjZdDM+KrKUwKwgPKMGgpPYYZcRZOInl9LSzyWhHKIDWjcoIPURd1AlUNVC0w+5H9BIkaVyrI8lxod8sU5gXYLjluxlZPp52MP1gpettVFNRRtPLsMmO91cwqg58/aeSKDZK2Xm7rknavW/gIc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/6/26 17:46, Feng Tang wrote: > On Fri, May 01, 2026 at 08:51:39PM +0200, David Hildenbrand (Arm) wrote: >> On 4/28/26 10:37, Feng Tang wrote: >>> Hi David, >> >> Hi! >> >> [...] >> >>> >>> Right for default kernel configs. >>> >>> In kernel/dma/Kconfig: >>> >>> config CMA_SIZE_MBYTES >>> int "Size in Mega Bytes" >>> depends on !CMA_SIZE_SEL_PERCENTAGE >>> default 0 if X86 >>> default 16 >>> >>> config CMA_SIZE_PERCENTAGE >>> int "Percentage of total memory" >>> depends on !CMA_SIZE_SEL_MBYTES >>> default 0 if X86 >>> default 10 >>> >>> >>> Yes. I thought about that, and didn't have good solution, and used this >>> given it's on a multi-numa-node machine, which may not be too bad >>> regarding memory usage. >> >> It sounds wrong given the existing config options. > > Yes, it is confusing. > >>> >>> Robin did concern about the memory usage for embedded/small devices in >>> v2 review, and we change to v3 to not affect them. >>> >>> >>> I agree :) >>> >>> >>> This sounds good to me, if no objection from others. Maybe default 64MB >>> or more. One good part is, all these setup is under protection of >>> CONFIG_DMA_NUMA_CMA. >> >> I cannot do the heavy thinking here because -EBUSY, but maybe you want a config >> option similar to CMA_SIZE_MBYTES/CMA_SIZE_PERCENTAGE that either controls that >> these sizes will be split over NUMA nodes, or another one, that sets the default >> for pernuma. > > Maybe a CMA_NUMA_SIZE_MBYTES? Maybe, I'm hoping some CMA DMA people have the capacity to provide input. > >> [...] >> >>> >>> My thought was 'struct cma' already have 'nid' member, and when CONFIG_NUMA=y, >>> it may be useful to save the 'nid' info instead of NUMA_NO_NODE for the default >>> cma area (cmdline like cma=XXG@YYG could make it on different node) >> >> Ah, yeah. It's a bit nasty that we have to handle the default area like that. >> >> Another sign that we probably shouldn't deal with the default area :) > > Yep, in v2 I didn't touch the default area, while Robin had a concern > that the v2 approach will bindly add an extra per-numa cma area for > the node which already has the default area, which will hurt those > small/embedded devices which has limited number of memory. Adding > the nid check is trying to keep the behavior of one node device > unchanged. > >>> >>> >>> Per my understanding, it won't. There is a cma_validate_zones() to prevent it >>> from crossing zones. >> >> It's a bit confusing, because it ignores other nids. > > I might have missed your point. Do you mean one cma are could have > multiple ranges? I don't know, it's confusing :) -- Cheers, David